Secondary batteries (secondary cells) such as Nickel-cadmium storage batteries, nickel-hydrogen batteries, or lithium ion batteries can be recharged any number of times during their useful lifetimes. It is widely known by persons skilled in the art that this recharging process must be performed under careful control to minimize the damaging affects to the storage battery. (For example refer to "Charging Storage Batteries: Extending Useful Life", Bob Williams, "Cellular Business" April, 1989, pp 44 to 49.)
At the beginning of secondary battery recharging technology, the process of recharging required as much as a number of hours. As consumer products powered by secondary batteries became more and more common, there arose a need for a system capable of charging times measured in minutes rather than hours.
While it is possible to fast charge a secondary battery, to prevent irreversible damage to the storage battery, the storage battery recharging process must be performed with even more care. (For example refer to "Latest Information on Nickel-Cadmium Batteries" in the report of the September 1990 Cadmium Society Brussels Seminar, published in November, 1990.)
Prior art has shown that a variety of systems have been developed for the fast recharging of secondary batteries. In these systems it has been standard to monitor the voltage and/or temperature of the storage battery being charged, and to interrupt or change the charging current applied to the storage battery when the temperature or voltage reaches a preestablished level. Typical prior art is described in U.S. Pat. No. 4,006,397 (Catotti et al).
Japanese patent publications Sho 62-23528 and Sho 62-23529 disclose a method for use in recharging of secondary batteries such as nickel-cadmium batteries, wherein the voltage waveform of the battery is observed during charging, a number of deflection points appearing in the voltage waveform being stored beforehand, and if the stored deflection points occurred in a given sequence, the charging process is interrupted. In this method, however, it is required for each type of battery to store beforehand the variations occurring in the voltage waveform of that type of battery during the charging process, and to change the stored contents before charging to contents appropriate to the type of battery to be recharged, not only making operation complex, but giving no assurance, by reasons of the charging environment and history of the battery, that the voltage output waveform of the battery would follow in sequence an a amplitude the stored information, thereby making it impossible to perform accurate charging and recharging, making it difficult to perform high-speed charging without causing loss of battery performance.
In addition to nickel-cadmium, nickel-hydrogen and lithium ion batteries exist as secondary batteries.
Previously the recharging of the above-mentioned secondary batteries, it required from 6 hours to even as much as 16 hours in some instances, and even with what was called fast charging at over a relatively short time, still required 1 to 2 hours.
In the past, although in recharging what were called rechargeable batteries or storage batteries for use in their intended purposes, it was known that it was desirable to make the charging time as short as possible, the limitations imposed by the rise in internal battery temperature and internal pressure in the battery caused by a chemical reaction within the secondary battery not only lead to destruction of the cells, but also to a deterioration of the electrical characteristics of the cells, that is, the output characteristics and charging characteristics, so that the method of charging by means of a large current over a short period of time was not used.
However, today the demand for secondary batteries is increasing in a large of number of applications in various industries, and in particular, there is a strong demand for secondary batteries for use in applications such as in environments in which machine tools are used, in medical and other equipment for hospitals, and in communications, such as in mobile telephones, applications which not only require that batteries do not run down during operation but also require fast or even instantaneous recharging.
If a graphical comparison is made of the above-mentioned voltage and temperature variations with respect to charge level during the charging of the various types of secondary batteries mentioned above, it can be seen that each type of battery exhibits unique characteristics, as shown in FIG. 2 to FIG. 4.
That is, the voltage and temperature characteristics of a nickel-cadmium storage battery are as shown in FIG. 2, the voltage and temperature characteristics of a nickel-hydrogen battery are as shown in FIG. 3, and the voltage and temperature characteristics of a lithium ion battery are as shown in FIG. 4.
For this reason, in the past, not only did the charging Of any type of secondary battery require a long period of time of at least one hour, but also it had the problem of requiring a change of the charging method or charging apparatus to suit the type of secondary battery, making the only charging methods available troublesome, time-consuming, and costly.
The purpose of the present invention is to improve the above-described shortcomings of the prior art, and to facilitate the recharging of secondary batteries, and in particular nickel-cadmium, nickel-hydrogen, and lithium ion secondary batteries, within an extremely short period of time of from several minutes to 20 minutes. Recharging at this extremely fast speed increases the significance of a number of parameters which were not so significant in the relatively slow-speed prior art recharging systems. However, it was discovered that these parameters could be processed so as to produce a recharging system which performs safe, high-speed charging without damaging side-effects to the storage battery being charged.
In the past, to charge secondary batteries which consist of mutually differing technical elements, and which have differing charging characteristics and behavior, it was necessary to make available separate chargers and to select the charger appropriate for charging the type of secondary battery to be charged.
Therefore, the charger was something to be used only for the charging of a particular type of secondary battery, it being necessary to make available individual chargers for individual secondary batteries, making the charging operation not only inconvenient, but troublesome and complex as well.
Even for the same type of secondary batteries, if an amount of charging current used in a charging operation, which is generally represented by a charge rate C, differ, the chargers would have to be provided separately, causing the problem of the heed to have a considerable number of charger types available.
However, with the demand for such secondary batteries increasing, and with a diversification in the fields and location in which secondary batteries are used, there has arisen an increasing need for a charger capable of use anywhere in charging any type of secondary battery completely within a short period of time, for applications requiring quick charging and immediate use of secondary batteries, such as in mobile data communications, mobile telephone communications, and at construction sites.
For this reason, the is a desire to have a single charger not only capable of charging a secondary battery of any type of construction, but also capable of charging under any charging rate C conditions. However, until the present, there has been no such practically usable charger.
Therefore, the object of the present invention is to improve on the defects described above, and provide a single charger which is universally usable to charge any type of secondary battery in a short period of time under any arbitrary charging rate C.